The risk of myopathy during treatment with drugs of this class is increased with concurrent administration of cyclosporin, fibric acid derivatives, niacin (nicotinic acid), erythromycin and azole antifungals.
Antacid: Co-administration of atorvastatin with an oral antacid suspension containing magnesium and aluminum hydroxides, decreased atorvastatin plasma concentrations approximately 35%. However, LDL-C reduction was not altered.
Antipyrine: Interactions with other drugs metabolized via the same cytochrome isozymes are not expected because atorvastatin does not affect the pharmacokinetics of antipyrine.
Colestipol: Plasma concentrations of atorvastatin decreased approximately 25% when colestipol and atorvastatin were co-administered. However, LDL-C reduction was greater when atorvastatin and colestipol were co-administered than when either drug was given alone.
Cimetidine: Atorvastatin plasma concentrations and LDL-C reduction were not altered by co-administration of cimetidine.
Digoxin: When multiple doses of atorvastatin and digoxin were co-administered, steady-state plasma digoxin concentrations increased by approximately 20%. Patients taking digoxin should be monitored appropriately.
Erythromycin/Clarithromycin: Co-administration of atorvastatin and erythromycin (500 mg four times daily), or clarithromycin (500 mg twice daily) known inhibitors of cytochrome P450 3A4, was associated with higher plasma concentrations of atorvastatin.
Oral Contraceptives: Co-administration of atorvastatin and an oral contraceptive increased AUC values for norethisterone and ethinyl estradiol by approximately 30% and 20%. These increases should be considered when selecting an oral contraceptive for a woman taking atorvastatin.
Warfarin: Atorvastatin had no clinically significant effect on prothrombin time when administered to patients receiving chronic warfarin treatment.